A polyolefin resin which is a polymer of an olefin monomer is widely employed in various uses since the polyolefin resin is excellent in mechanical properties and chemical resistance, and it can easily be subjected to forming at a small cost. Moreover, the uses of the polyolefin resin are further being expanded with global environmental problems in recent years as its background since the polyolefin resin is superior in the ease of recycling.
On the other hand, it is known that the coating or adhesion of a paint to the surface of a polyolefin resin molded product is difficult since the polyolefin resin is nonpolar. Accordingly, when coating or adhesion of a paint to the surface of a polyolefin resin molded product is carried out, a method has generally been adopted in which the surface of the polyolefin resin molded product is subjected to a surface treatment such as a plasma treatment, flame treatment, UV-light irradiation treatment, and chromic acid treatment in advance to activate the surface thereby improve the adhesion of a paint.
However, it makes the coating process complicated, requires a large facility expense, and causes a time loss to conduct such extra surface treatment. Besides, the method for the surface treatment has such an inconvenience as an unevenness in the effect of the surface treatment is ready to produce by the difference in the shape or size of the molded product or by the effect of a pigment or additive contained in the polyolefin resin.
As a method for coating the surface of a polyolefin resin without performing the surface treatment described above, a method is known in which a chlorinated polyolefin having a strong adhesive force to a polyolefin resin is used as a primer (a lower layer of coating) and an acrylic resin or the like is used as the top coat (the upper layer of coating). For instance, as a paint having a good adhesive property to a polyolefin resin, a paint of a resin composition comprising a chlorinated polyolefin and an acrylic copolymer at a ratio of 10:90 to 90:10 is disclosed in Japanese Examined Patent Application, Second Publication No. Sho 63-24628 (Japanese Unexamined Patent Application, First Publication No. Sho 58-176207).
However, in the paint described above, a chlorine-containing compound is used, and thus the use of the paint tends to be avoided from an upsurge of interest in environmental problems in recent years. Therefore, the demand for a primer composition used for coating and containing no chlorine has rapidly been raised in these days.
Further, it is lately been required to provide a primer composition used for coating and having excellent adhesive properties even to such a resin as an acrylic resin in addition to a polyolefin resin.